BIACORE device

Biosensors based on optical fibers as transduction element have been recently reviewed by Wolfbeis [97]. Optical biosensors based on miniattaized SPR or on evanescent field monitoring are not as often found in miniaturized biosensors, especially in comparison to miniaturized electrochemical transducers, yet. Two examples will be given here a miniaturized SPR biosensor by Cullen and co-workers [98] and an evanescent based microchip biosensor by Borchers and co-workers [99]. The best-known SPR biosensor is the BIAcore device from Pharmacia Company, Sweden. It has been on the market for over a decade and is routinely used for hybridization kinetic analyses, specificity analyses, etc. Cullen and co-workers have incorporated a commercially available miniaturized SPR transducer into a field analyzer and developed a competition and inhibition assay for an estrogenic compound in water samples that function as endocrine disrupting compounds (EDCs). 

BIACORE devices presumably deliver the best values for the kinetic constants kon and koff—and with this the Kd, the affinity constant (see Section 2.3.2). 

BIACORE devices capture bindings of low affinity (Kd up to about 10 pM). 

It takes about one to two weeks to become familiar with the BIACORE device, and then even beginning graduates can count on experiencing success. Two users reported to me (with a sparkle in their eyes) very reproducible, great. So much for the good news. Now let s examine the problems. 

In most existing publications with BIACORE devices, both binding partners were... 

If you still cannot measure any binding, or if you were not able to label the ligand, you should beg for a few days of access to a BIACORE device or an isothermal calorimeter. If that also leaves you depressed, it is time to study Section 2.2.6. 

Very few immunosensors are commercially available. The commercial immunosensors are either the detector or bioanalyzer types. The PZ 106 immunosensor from Universal Sensors Inc. (New Orleans, LA) has been used as a detector to measure antibody-antigen reaction. Ohmicron (Newtown, PA) developed a series of pesticide immuno-bioanalyzers that have been used in field tests. Pharmacia Biosensor USA (Piscataway, NJ) recently introduced BIAcore immunodetection system. A combination of a unique flow injection device and surface plasmon resonance (SPR) detection technique provides a real time analysis. A carboxylmethyldextran layer added to plasmon generating gold film is a hydrophobic, activatable, and flexible polymer that provides high antibody and low non-specific bindings. System demonstration at the Institute of Food Technologists (IFT) 1994 meeting in Atlanta drew attention of food scientists. It should easily be adapted for food protein characterization. 

The first commercial SPR was launched hy Pharmacia Biosensor AB (presently Swedish BIAcore AB) in 1990. Since then, the device has been refined and now BIAcore [37] offers several models (BIACORE 3000, BIACORE 2000, BIACORE 1000, BIACORE X, J, Q, S51, and C models). The biosensors of BIACORE 1000 to 3000 are fully automated instruments, with a disposable sensor chip, an optical detection unit, an integrated micro-fiuidic cartridge, an autosampler, method programming and control software. Less expensive manually controlled alternatives cU e the BIACORE x and BiacoreQuant . 

Figure 2.6. Binding with BIACORE the core of the device.

The device delivers the kinetics not in single points but as a continuous exact curve. The continuous injection maintains a steady ligand concentration on the chip throughout the measuring time. Depending on the model, the application of the sample is automatic or at least semiautomatic and is evaluated by computer. In short, he is happy who measures with BIACORE. 

Commercial biosensors are available in several forms such as autoanalysers, manual laboratory instruments and portable (handheld) devices. One biosensor system, Biacore Q (Biacore, Uppsala, Sweden), is based on optical detection— the SPR technique for vitamin B12 analysis. 

In essence, this technique allows for the detection of surface binding interactions in real time without the use of labels. Immunosensors that rely on these principles are commercially available from Biacore AB (formerly Pharmacia Biosensor). These are based on the popular BIACORE 3000, BIACORE 2000 and BIACORE probe instruments in conjunction with disposable sensor chips, which may be purchased with affinity capture chemistries in place (e.g. SA5 Sensor Chips with streptavidin bearing surfaces for capture of biotinylated compounds) [92]. These devices incorporate micro-fluidic systems for delivery of reagents required for analysis and are capable of measuring affinities and kinetics of antibody-antigen interactions in addition to analyte concentrations, which can be determined to the picomolar range [93]. 

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